Animating transparency of an object with an alpha channel applied
Two images above are a black transparent texture named Texture.003. Not the Show.

In the materials texture panel create a blend texture with Colors Ramp Selected True.  Solid black 100% transparent on both ends of color ramp.

Select Influence Alpha.  Alpha of 0 is 100% transparent as you know.  We are affecting the final value with our new alpha target value at 0.0 .  If we [were] targeting with a new alpha value of 1.0 we would have an opposite affect.  This is mentioned to keep the influence idea separate from the actual alpha value of the texture pixel alpha.

Create animated value from 0.0 to 1.0 on the appropriate keyframes with alpha. Blend Type Multiply.  The yellow numeric background indicates a value with a keyframe.



Image above. Shows texture in first slot which has transparent pixels.  The sphere was only to avoid a solid black background.